The invention relates to the transmission of voice over IP (VoIP, Voice over Internet Protocol) in wireless telecommunications systems and especially to changing the radio access gateway managing the voice over IP connection in wireless telecommunications systems.
Voice over IP, i.e. speech transmission utilising the IP protocol, has received a great deal of notice during the last few years. H.323 is a standard defined by ITU (International Telecommunication Union) for packing the voice data and video image used in video conferencing programs and for call control, and it is one of the most important standards for implementing voice over IP. The H.323 standard specifies the transfer of packet-based multimedia information in systems which do not necessarily guarantee the quality of service (QoS). The H.323 standard can be applied to any IP-based (Internet Protocol) network, such as the Internet. H.323 can be used in both point-to-point calls and different point-to-multipoint applications. H.323 is a part of a larger collection of standards, the H.32X standards, which define conferencing standards for different network types. H.323 is designed to work with all H.32X recommendations.
Another standard used for voice over IP implementation is SIP (Session Initiation Protocol) developed by IETF (Internet Engineering Task Force). SIP is an application-level control protocol which allows the establishment, alteration and interruption of multimedia connections and voice over IP connections. The H.248/Megaco standard for gateways developed by ITU and IETF together can also be used in voice over IP implementation.
Radio access gateways (RAGW) are used in wireless telecommunications systems to transmit data between a wireless network and an IP-based network, i.e. to perform protocol conversion between a voice connection provided for wireless terminals and voice over IP in an IP network.
Current standards used in voice over IP do not themselves provide support for a handover of an active voice connection of a terminal. In this application, the term ‘handover’ refers to changing the radio traffic channel and responsibility from a source system to a target system in such a manner that a data transmission connection is maintained for the user's service. Handover can take place due to the moving of the terminal or for other reasons, such as for balancing the load between cells. One or more base stations are typically connected to radio access gateways, i.e. associated with them, the radio access gateways managing the voice connections of terminals in the areas of the base stations. If there is a need for a handover to a base station connected to a different radio access gateway, the radio access gateway transmitting data also needs to be changed.
Because every radio access gateway typically has its own IP address, changing the used radio access gateway would require changing the IP address at the sender end. This could be done by directing the media streams from the sender to a new radio access gateway and by excluding the old radio access gateway from the connection provision. A big problem with mobility support in standards used for voice over IP is that the apparatuses do not support any kind of signalling related to changing the termination point of the connection. Thus, the terminal of a second termination point cannot be configured during an active connection to use a new radio access gateway without a noticeable decrease in the speech quality during the handover. Voice over IP connections are typically arranged through firewalls which are quite problematic when the termination point is changed. Changing an active connection requires quick action from the firewall and understanding the signalling related to the handover, because the destination IP address may change during the call.